Aluminum soap hydrocarbon thickener with increased solvation



carbon liquid Without Unite ALUMINUM SOAP HYDROCARBjON THICKENER WITHINCREASED SOLVATION Rudolph R, Leverberg, Metuchen, and Frederick NeilBaum'gartner, Plainfield, N.J.,'a'ss'i'gnors to Esso Research andEngineering Company, a corporation of Delaware a No Drawing. Filed Oct.22, 1956, Ser. No. 617,662

6 Claims. (Cl. 252-'-"-37) This invention relates to the production ofimproved basic metal soaps of aliphatic carboxylic acids for use asthickeners of hydrocarbon oils. It relates more particularly to theimprovement-of basic aluminum disoaps formed from relatively lowermolecular weight aliphatic or fattyacids by addition of minor or smallamounts of less water-soluble higher aliphatic and fatty acids after theprecipitation or dispersion of the soaps but before filtration andwashing.

In a conventional preparation of the soaps useful for hydrocarbonthickening purposes, a water-soluble salt' referred to as alm, such asaluminum sulfate, aluminum chloride, etc. is added for precipitating thealuminum soap from the alkaline aqueous solution of an alkali metalsalt. After precipitation, the soap precipitate is filtered, washed,then dried. It has been found that in usingaliphatic or fatty acids ofrelatively low molecular weight, e.g l the G acids, such as 2-ethylhexoic acid or other such acids in the range of C to C the thickeningsoap product formed does not gel a hydroprolonged mixing and thus isunsatisfactory.

A significant product evaluation test for determining the rate of gelformation of the thickening soaps is known as the vortex time. Thevortex time is a measure of time in minutes for thickening a givenhydrocarbon liquid to a point where settling of the thickening soap Willnot occur. In this testthe thickening soap is added rapidly to theorganic solvent (e.g. gasoline) which isto be thickened while themixture is stirred at a controlled speed and temperature. Short vortextimes are generally desirable For example, thickening soaps which givevortex times up to 10 minutes are acceptable, although soap productswhich give vortex 7 times less than 10 minutes are much more desirable.Many commercially produced soap thickeners on the same basis have beenfound to possess vortex times of 30 minutes or longer and are thusunsuitable. Many thickeners on aging have been found to have theirvortex times increasedto well over 10 minutes and thus become quiteunsuitable. I

. By analysis of thickening soap products found to give long'v'or't'extimes or to show poor sol'vation in hydrocarbon liquids, 'it'was discovered that such products possessed a low free fatty acidand ahigh excess hydroxide content, which for analytical purposes isexpressed in terms of AM OH) In other words, the mole ratio of the freeacid (FA,-to saidex cess hydroxide content, Al( OH) 3 3 is low, and atthe same time, the excess hydroxide content of the soap is high. Thereare indications from the studies of the soaps, that those formed fromaliphatic or fatty acids having appreciable solubility in water have thefree organic acids removed inthe washing step, leavingunreactedhydroxide to render the soap particles more impervious to the action ofsolvents which States Patent ice are to be gelled. The soap particlesleft more imper'vious to the action of the solvents on contact with 'thehydrocarbon or other organic solvents have a lower or fatty acid havinga higher molecular weight and less water-solubility.

Examples of aliphatic or fatty acids of higher molecular weight and lesswater-solubilityuseful for improving the thickening soaps formed fromthe lower molecular weight organic acids are such as obtained from thenaturally occurring coconut oil, which include principally acids havingabove 8 carbon atoms per molecule, e.g. capric, lauric, myristic,palrnitic, stearic, oleic, linoleic dimerized linole'ic, etc. Other highmolecular weight fatty acids, like those-in coconut fatty acids, areobtainable from plant and animal sources, e.g. palm kernel oil, andanimal fats. The higher molecular weight aliphatic carboxylic acids mayalso be produced synthetically as by oxidation of hydrocarbons,aldehydes, etc. and may be obtained from petroleum oils, e.g. naphthenicacids.

For the sake of brevity, all of the organic acids that are of use,including fatty acids and aliphatic carboxylic acids, straight chain,branched chain, cyclic, saturated and unsaturated, will be referred toas aliphatic acids.

Since the higher acids may be added to the soaps of the lower aliphaticacids for their improvements after the lower aliphatic acid soaps havebeen precipitated, the higher acids need not react to form the soapsthemselves. The higher acids are advantageously added after theprecipitation, but before filtering, and before washing, and are notremoved by the washing to any substantial extent.

The quantity of higher organic acids added to the precipitatedthickening soaps formed from the lower acids can be economically kept toa minimum depending on the excess hydroxide content of the soap to beimproved. In general, sufiicient amount of the higher acid is preferablyadded to give an FA/Al(OH) molar ratio of from 0.1 to 1.0. At the sametime, the quantity of excess hydroxide present will determine at whichpoint in this range the ratio of the free acid to the excess hydroxidein the product should lie. For example, normal soapproducts whichcontain small amounts of excess hydroxide, are improved by adding thehigher acid to make the FA/AL(OH)'3 mole ratio be in the range of 0.1 to0.5 approximately; while the soap products having a somewhat higheramount of excess hydroxide, e.g'. more than 1% by Wt. calculated asAl(OH) are im proved in their solvation rate (decreased vortex time) byadding sufiicient higher acid to give the soap an FA/AI(OH)3 mole ratioin the range of approximately 0.5 to 1.0.

An illustration of the foregoing method of improv- Soap A-Aliimintnnethyl hexoate, soap by normal preparation. Soap BeAluminum ethylhexoatesoap by normal preparation plus 0.8 wt. percent coconut acids addedprior to filtration and washing.

It is to be observed that the addition of the small amount of coconutacids for obtaining the improved Soap B brought the percent of excesshydroxide down below approximately 1.0% as Al(OH) and increased theFA/AI(OH) mole ratio to above 0.1, thereby reducing the, vortex time by50% to an acceptable minutes without appreciable change in the gelstrength or consistency. In any event, the gel strength or consistencyremained at a satisfactory level so long as the amount of added acid wasnot excessive.

It is to be understood that various components of the coconut oil acidsor similar fatty acids from other sources and their mixtures may beused; The best amounts of the coconut acids to be added similarly shouldbe determined for each soap which is to be improved in accordance withthe present invention.

To estimate the free fatty acid in the soap, the soap is extracted witha suitable selective extraction solvent. Isooctane has been used atlow-temperatures, but a better solvent is anhydrous dimethylformamidewhich extracts the free fatty acid at ordinary temperatures in the rangeof to 40 C. without dissolving the thickener even on prolonged standing.One or more extractions may be made with the solvent to remove all thefree fatty acid from a given sample. Two extractions with anhydrousdimethylformamide are sutiicient to remove all free fatty acid sincesubsequent extractions showing no titratable acid indicate a completeremoval of the free acid with no decomposition of the thickener. Ofcourse, the soaking in the solvent could be excessive; therefore, it wasfound best to use four successive extractions. The extractions arecarried out rapidly to insure a minimum of decomposition. The extractionmay be carried out by placing a weighed amount of the soap thickener ona sintered support in a glass funnel fitted into the upper part of afilter flask. Using a 2 gram sample, ml. anhydrous dimethylformamide isadded to the funnel to pass through the soap in finely divided and wetcondition. Vacuum may be applied to expedite passage of the solventthrough the sample. Additional similar amounts of the solvent are addedfor repeating the above step three more times, although for some soapstwo extractions are sufficient. 10 ml. distilled water is added for eachextraction and 3 to 4 drops of phenolphthalein are added. The dilutedcombined extracts containing the indicator are then titrated with 0.1NaOH to an end point stable for 15-20 seconds. A blank, similar solutionof the solvent containing no extract is titrated. The percent free fattyacid (PA) is then found by the following calculation:

(Ml. NaOH for samples I -m1. NaOH for blank) 14.42XN NaOH Sample weight;=percent free fatty acid (FA) (as eaprylic acid) The total fatty acidcontent of the soaps is determined by decomposing a soap with HCl ofdetermined amount and the liberated fatty acid extracted is titratedwith a standardized sodium hydroxide solution in a well-known manner.

The use of anhydrous dimethylformamide as a selective solvent forremoving the free organic acids from the thickening soaps is describedand claimed in an application, Serial Number 617,663, filed October 22,1956, now US. Patent No. 2,884,430, for F. N. Baumgartner.

The percentage of excess hydroxide as Al(OI-I) can be determined byanalyzing for the total aluminum in the soap, then subtracting from theequivalent total Al(OH) the amount of the aluminum combined withthe'fatty acid as in a disoap. The total aluminum content of the soapcan be determined by the classical hy-' droxide precipitation andignition method. In this analysis an addition of an ashless whitemineral oil to the precipitate prior to ignition prevents loss ofpowder. All organic material is burned to leave the aluminum oxideresidue by heating the ignition residue for 4 to 6 hours 4 in a mufflefurnace at 1600" F. The calculation of the percentage AI(OH) is given asfollows:

In the above formula (RG0 represents the radical of the fatty acidcombined with the aluminum which is also combined with the hydroxidegroup (OH).

The aluminum soaps can be prepared by the addition of aqueous solutionsof aluminum salts to solutions of sodium or potassium soaps of the fattyacids in the presence of excess alkali. The term excess alkali refers tothe amount of alkali hydroxide used over that required forsaponification. The aluminum soaps can be prepared in nonaqueoussolvents by reaction between fatty acids and aluminum alkoxides. Soapshave been prepared in this way from acetic acid and higher fatty acids,both saturated and unsaturated, acyclic and cyclic. There are othervariations in the preparation of the soaps, but the present invention isnot concerned with the steps of making the soap except with regard tothe improvement of increasing the FA/A1(OH) mole ratio. e

For the purpose of comparison preparation of soaps from lower fattyacids were made in accordance with the following example:

Example To a measured amount of distilled water, 4243 grams, in thereaction vessel was added a calculated amount of sodium hydroxide (4.5moles for 3.0 moles of Z-ethyl hexoic acid). When all the caustic haddissolved, the required amount of Z-ethyl hexoic acid, i.e. 3.0 moles,was added. The resulting soap solution was stirred for 10 to 15 minutesand brought to the desired temperature of 35 c. The alum solution(2.18%) Al,(s0,) -18H 0 was then added at a controlled rate. The alumsolution was made up of 0.86 mole of the aluminum salt and TABLE 11Percent I 'Vortex Soap Thickener Al(OH)3 FAIAI(OH)3 'lll llrrle,

Commercial Soap-0 2. 5 0.031 55 Experimental Soap-D l. 7 0. 045 20 Thecomparison in Table II shows that the low FA/Al(OH) ratio and highpercentage of Al(OH);, gave the commercial product the undesirable highvortex time of 55 minutes. Even the freshly prepared Soap-D by theconventional procedure could be improved in accordance with the presentinvention.

The variations and deficiencies of the different commercial products maybe due to a number of factors. The high excess hydroxide and low freefatty acid contents may be originally due to incomplete reaction duringprecipitation followed by overwashing. Incomplete reaction may be causedby a multitude of factors, including inadequate mixing, incorrectaddition of the alum, and prolonged hydrolysis. As stated, with agingfor several months the condition of the thickener becomes (13)Filtration, preferably by centrifuge. I (.4) Redrying to the desiredmoisture content.

'ment 'with an aliphatic carboxylic or fatty acid of relativelylow-water solubility and thereby are made to meet specific requirementswithout altering or damaging other desirable properties appreciably. Thefatty acid treatment of the soaps involves the following steps:

(1) Dispersion of the poor soap thickener in suitable medium, preferablywater.

(2) Addition of the aliphatic acid having a relatively low watersolubility, preferably ofhigher molecular weight than the acid used informing the soap.

It is apparent that the method of dispersing the soap to be improved inwater is immaterial as long as adequate dispersion is obtained. When thefreshly prepared soap is being improved, the addition of the highermolecular weight fatty acid is made to the precipitated soap prior tofiltering. Any satisfactory filtering and drying technique may be usedwithout deviating from the objects of the invention.

The quantity of fatty acid which is added depends I largely on thefollowing factors:

(a) The molecular weight and acid saponified:

(b) The excess (OH) content of the soap:

() The free acid content of the soap.

The last two quantities may be determined from the total aluminumanalysis, total fatty acid, and free fatty acid analysis, as previouslydescribed. In general, it is desirable to make the soap contain a totalfree fatty acid (including aliphatic acid added) to excess hydroxidemole ratio in the range of 0.05 to 1.0. However, the exact amount offatty acid to be added and the exact ratio of FA/Al(OH) is readilydetermined by experiment so that the quantity of the fatty acid added ischanged until the product gives the desired vortex time.

The following examples additionally show how the invention has beendemonstrated and applied.

A variety of commercial soaps showing poor solvation properties, i.e.high vortex times, were treated with coconut acids in amounts of,0.,87%to 1% by weight based on the dry soap samples. The soap samples werefirst'dispersed in water, a 150 gram sample being mixed with 1800 ml. HO using a dispersator. sion mixtures 1.3 g. of coconut acids were addedand water-solubility of the To the dispermixing was continued. Themixture was then filtered by centrifuging and the soap product separatedfrom liquid was dried at 49 C. for 2% hours in a forced draft oven. I

The following comparative data is representative of the improvement madeby adding the coconut fatty acids:

The hydrocarbon oil thickening soaps, methods for their preparation, andthe uses are well known and the present invention is not concernedtherewith except for the improvement which is described and claimedherein. The thickening soaps are used as thickeners or gelation agentsin various hydrocarbon liquids, e.g. gasoline, naphtha, kerosene, heatoil, lubricating oils, other distillates, and mixtures of suchdistillates, which also may contain other dissolved or dispersedmaterials. The soaps are considered to be polymeric in structure, bothin the solid state and in hydrocarbon solution. They are characterizedby their ability to form with'hydrocarbon .oil, gels of high viscosity.7

Usually the aluminum disoaps requiring solvation improvement have, beenfound to contain less than 1 wt.

percent and even less than 0.5 wt. percent free aliphatic acidscorresponding to the aliphatic acids combined in .the soap. These soaps.have been well improved in solvation properties by adding 0.5 to about1 wt. percent of an aliphatic acid, preferably an aliphatic acid moredifiicult to wash out.

In the solvation improved disoap products, the basic aluminum disoapunits may be represented by the formula:

wherein (RG0 is a carboxylic radical of an aliphatic acid, RCOOH, havingappreciable water-solubility, e.g. Z-ethylhexoic acid or isooctoicacids, R thus being an ali phatic hydrocarbon group of 7 carbon atoms.Associated with the disoap units are units containing more than one (OH)group for each aluminum atom and these are the excess hydroxide groups.A small amount of the aliphatic acid, RCOOH, having appreciablewater-solubility will tend to be present as free acid, eg. occluded bythe disoap units. To achieve improved solvation, the total free acidspresent is made to include another aliphatic carboxylic acid of stilllower water-solubility, and thus generally, of higher molecular weightthan the acid combined in the disoap. Moreover, frequently the acid oflower water-solubility added to increase the total free acid content ofthe disoap product will be present in higher proportion of the totalfree acid than the aliphatic acid indicated to be mainly combined in thedisoap.

What is claimed is:

1. The method 'of improving a hydrocarbon oil soap thickener insolvation properties, said soap being a basic aluminum disoap of analiphatic carboxylic acid having 8 to 10 carbon atoms per molecule whichcomprises dispersing said'soap thickener in a liquid medium in which thesoap is not soluble, adding to the thus dispersed soap thickener analiphatic 'carboxylic acid of relatively higher molecularweight and oflower water solubility than the acid in the disoap in relatively smallamount to increase free aliphatic carboxylic acid content of the soap,filtering I and washing the soap thus increased in free acid content andrecovering a soap that has a mole ratio of total free aliphaticcarboxylic acid to excess hydroxide of 0.05 to 1.0.

2. The method as described in claim l wherein the soap thickener isaluminum di-Z-ethyl hexoate, the liquid medium is water, and the addedhigher molecule weight aliphatic acid is a coconut oil acid having morethan 8 carbon atoms per molecule.

TABLE I11 Gel Sample Vortex Strength, Time 2% at Commercial Soap 50 260Treated Soap 7 280 V In the above table the treated commercial soap wasmadeby adding 0.87% coconut fatty acids: The treated soap was given avery satisfactory lowered vortex time of 7 minutes. 'This treated soaphad unimpaired gel I strength. Similar tests were made using an. addedwet- 1 ting agent and-the improvement by the added fatty acid 'wasrofsimilar order. It. is to be understoodthat the 7 examples given are forthe purposeof illustration, and j v are not intended to limit the scopeof the invention.

3. The method of improving the solvation properties of a hydrocarbon oilsoap thickener which comprises adding a water-soluble aluminum salt toan alkali metal salt of molecule and a lower water solubility than saidC to C1 aliphatic carboxylic acid -to obtain a mole ratiooftotal freealiphatic carboxylic, acid to excess hydroxide of 0.05 .v

*7 to 1.0 in said aluminum soap, filtering and washing said aluminumsoap with a substantial quantity of water and drying said aluminum soapprior to mixing it with said hydrocarbon oil. p p

4. The method as described in claim 3 wherein the C to C aliphaticcarboxylic acid used to prepare the aluminum soap contains 8 carbonatoms per molecule.

5. The method as described in claim 3 wherein the C to C aliphaticcarboxylic acid used to prepare the aluminum soap is Z-ethyl hexoicacid.

6. The method of improving the solvation properties of a hydrocarbon oilsoap thicknener which comprises adding a water-soluble aluminum salt.to' an alkali metal salt of a C aliphatic carboxylic acid Whereby analuminum soap of said C aliphatic carboxylic acid is precipitated,adding about 0.5 to 1 weight percent of coconut aliphatic carboxylicacid to said aluminum soap filtering and washing said aluminum soap witha substantial quantity of Water and drying said aluminum soap prior tomixing it with said hydrocarbon oil.

' 8 References Cited in the file of this patent UNITED STATES PATENTS2,264,353 Zimrner et a1. -4. Dec. 2, 1941 2,280;474 Brykit et a1 Apr.21, 1942 2,380,893 Zimmer et al. ]uly'31, 1945 2,384,551 Jehleept.11,1945 2,606,107 Fieser Aug. 5, 1952 2,618,596 Minich et a1. Nov.18, 1952 2,741,629 Cohen Apr. 10, 1956 2,751,283 Van Strien et a1. June19, 1956 2,751,361 Van Strien et al. June 19, 1956 2,758,123 Mason et a1Aug. 7, 1956 OTHER REFERENCES Metallic Soaps for Greases, article byElliot, The Oil and Gas Jour., November 1, 1947, pp. 63-82.

The Jour. of the Amer. Oil Chemists Soc., article by Smith et al., vol.26, March 1949, pages 135-138.

1. THE METHOD OF IMPROVING A HYDROCARBON OIL SOAP THICKENER IN SOLVATIONPROPERTIES, SAID SOAP BEING A BASIC ALUMINUM DISOAP OF AN ALIPHATICCARBOXYLIC ACID HAVING 8 TO 10 CARBON ATOMS PER MOLECULE WHICH COMPRISESDISPERSING SAID SOAP THICKENER IN A LIQUID MEDIUM IN WHICH THE SOAP ISNOT SOLUBLE, ADDING TO THE THUS DISPERSED SOAP THICKENER AN ALIPHATICCARBOXYLIC ACID OF RELATIVELY HIGHER MOLECULAR WEIGHT AND OF LOWER WATERSOLUBILITY THAN THE ACID IN THE DISOAP IN RELATIVELY SMALL AMOUNT TOINCREASE FREE ALIPHATIC CARBOXYLIC ACID CONTENT OF THE SOAP, FILTERINGAND WASHING THE SOAP THUS INCREASED IN FREE ACID CONTENT AND RECOVERINGA SOAP THAT HAS A MOLE RATIO OF TOTAL FREE ALIPHATIC CARBOXYLIC ACID TOEXCESS HYDROXIDE OF 0.05 TO 1.0.